Image position correcting optical system

ABSTRACT

Disclosed is an image position correcting optical system, comprising sequentially from an object side, a first lens group having positive refracting power and a second lens group having negative refracting power. The first lens group is fixed. The second lens group is so provided as to be movable along an optical axis. A part of lens subunits of lens elements constituting the first lens group is so provided as to be movable in a direction across the optical axis. A positive lens element of the lens elements constituting the first lens group satisfies the following conditions: 
     
         1.43≦n.sub.d ≦1.65 
    
     
         65≦ν.sub.d ≦95 
    
     
         0.302≦θ.sub.FCd ≦0.309 
    
     where n d  is the refractive index with respect to the d-line, n F  is the refractive index with respect to the F-line, n c  is the refractive index with respect to the C-line, ν d  is the Abbe number with respect to the d-line, and θ FCd  is the partial dispersion ratio expressed by (n d  -n c ) / (n F  -n c ).

This is a division of application Ser. No. 08/363,823 filed Dec. 27,1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an image position correctingoptical system and, more particularly, to an optical systemincorporating a function to correct a fluctuation in an image positionthat is derived from a shake of a lens.

2. Related Background Art

In the present specification, a "correction of an image position" meanscorrecting a fluctuation in the image position due to a shake or thelike by displacing a certain lens unit in a direction across an opticalaxis.

In a conventional image position correcting optical system, as disclosedin the specification of U.S. Pat. No. 4,907,868, the number of lenselements constituting an image position correcting lens unit is as largeas 4, enough to occupy a space that is elongate along the optical axis.As a result, there increases a size of a drive actuator for displacingthe image position correcting lens unit in a direction substantiallyorthogonal to the optical axis.

Further, according to an image position correcting optical systemdisclosed in the specification of U.S. Pat. No. 4,978,205, the imageposition correcting lens unit is composed of three pieces of lenselements, but a secondary chromatic aberration is not compensated.

As explained above, the conventional image position correcting opticalsystem presents such inconveniences that the image position correctinglens unit is constructed of a large number of lens elements, and thedrive actuator of the image position correcting lens unit and, in turn,the optical system as a whole increase in size.

Also, if down-sizing is attained to some degree by reducing the numberof lens elements constituting the image position correcting lens unit,the compensation of the secondary chromatic aberration is insufficient,resulting in such an inconvenience that an imaging performance is poor.

SUMMARY OF THE INVENTION

It is a primary object of the present invention, which was devised inview of the problems given above, to provide a small-sized imageposition correcting optical system in which a secondary chromaticaberration is well compensated.

To accomplish the above object, according to one aspect of the presentinvention, there is provided an image position correcting opticalsystem, comprising sequentially from an object side: a first lens grouphaving positive refracting power; and a second lens group havingnegative refracting power, wherein the first lens group is fixed, thesecond lens group is so provided as to be movable along an optical axis,a part of lens subunits of lens elements constituting the first lensgroup is so provided as to be movable in a direction across the opticalaxis, and a positive lens element of the lens elements constituting thefirst lens group satisfies the following conditions:

    1.43≦n.sub.d ≦1.65

    65≦ν.sub.d ≦95

    0.302≦θ.sub.FCd ≦0.309

where n_(d) is the refractive index with respect to the d-line, n_(F) isthe refractive index with respect to the F-line, n_(c) is the refractiveindex with respect to the C-line, ν_(d) is the Abbe number with respectto the d-line, and θ_(FCd) is the partial dispersion ratio expressed by(n_(d) -n_(c))/(n_(F) -n_(c)).

Further, to accomplish the above object, according to another aspect ofthe present invention, there is provided an image position correctingoptical system, comprising sequentially from an object side: a firstlens group having positive refracting power; a second lens group havingnegative refracting power; and, a third lens group having positiverefracting power, wherein the first lens group is fixed, the second lensgroup is so constructed as to be movable along an optical axis, thethird lens group is so constructed as to be movable in a directionacross the optical axis, and a positive lens element of the lenselements constituting the first lens group satisfies the followingconditions:

    1.43≦n.sub.d ≦1.65

    65≦ν.sub.d ≦95

    0.302≦θ.sub.FCd ≦0.309

where n_(d) is the refractive index with respect to the d-line, n_(F) isthe refractive index with respect to the F-line, n_(c) is the refractiveindex with respect to the C-line, ν_(d) is the Abbe number with respectto the d-line, and θ_(FCd) is the partial dispersion ratio expressed by(n_(d) -n_(c))/(n_(F) -n_(c)).

To accomplish the above object, according to still another aspect of thepresent invention, there is provided an image position correctingoptical system, comprising sequentially from an object side: a firstlens group having positive refracting power; a second lens group havingnegative refracting power; and a third lens group having positiverefracting power, wherein the first lens group is fixed, at least onelens element having negative refracting power in the second lens groupis so constructed as to be movable along the optical axis, at least onelens element having positive refracting power and at least one lenselement in the third lens group are so constructed as to be movable inthe direction across the optical axis, and a positive lens element ofthe lens elements constituting the first lens group satisfies thefollowing conditions:

    1.43≦n.sub.d ≦1.65

    65≦ν.sub.d ≦95

    0.302≦θ.sub.FCd ≦0.309

where n_(d) is the refractive index with respect to the d-line, n_(F) isthe refractive index with respect to the F-line, n_(c) is the refractiveindex with respect to the C-line, ν_(d) is the Abbe number with respectto the d-line, and θ_(FCd) is the partial dispersion ratio expressed by(n_(d) -n_(c))/(n_(F) -n_(c)).

Generally, in the case of correcting a fluctuation in the image positiondue to the shake or the like by displacing a certain lens unit in thedirection substantially orthogonal to the optical axis, if thedown-sizing of the whole optical system is attained by reducing thenumber of the lens elements constituting the image position correctinglens unit, the imaging performance when correcting the image position isinferior to the imaging performance before correcting the imageposition.

According to the present invention, in a lens layout of a telephoto typeoptical system, there are discovered the conditions for ensuring thesufficient imaging performance in terms of practical use even whencorrecting the image position.

Hereinbelow, the conditional expressions will be explained in greaterdetail.

According to this invention, each positive lens element among the lenselements constituting the first lens group satisfies the followingconditional expressions (1) to (3):

    1.43≦n.sub.d ≦1.65                           (1)

    65≦ν.sub.d ≦95                            (2)

    0.302≦θ.sub.FCd ≦0.309                 (3)

where

n_(d) : the refractive index with respect to the d-line (λ=587.6 nm),

ν_(d) : the Abbe number with respect to the d-line, and

θ_(FCd) : the partial dispersion ratio.

Note that the partial dispersion ratio θ_(FCd) is expressed by thefollowing formula:

    θ.sub.FCd =(n.sub.d -n.sub.c)/(n.sub.F -n.sub.c)     (a)

where

n_(F) : the refractive index with respect to the F-line (λ=486.1 nm),and

n_(c) : the refractive index with respect to the C-line (λ=656.3 nm).

The conditional expressions (1) through (3) provide conditions forprescribing proper ranges of the refractive index, the Abbe number andthe partial dispersion ratio with respect to each positive lens elementamong the lens elements constituting the first lens group, making themass productivity preferable and compensating the secondary chromaticaberration well.

In the telephoto type optical system based on the inner focus method, orthe rear focus method, the movable lens group having negative refractingpower magnifies an aberration of the fixed lens group having positiverefracting power. Hence, for preferably compensating the chromaticaberration with respect to the whole optical system, it is of importanceto compensate the chromatic aberration of the fixed lens group havingthe positive refracting power as much as possible by itself. That is,each positive lens of the first lens group is required to satisfy theabove conditional expressions (1) through (3) in order to adequatelycompensate the chromatic aberration that will otherwise probably turnout to be a critical defect to the telephoto lens.

For obtaining a much better imaging performance, according to thepresent invention, it is preferable that the following conditionalexpression (4) be satisfied:

    0.2≦φ.sub.1 /|φ.sub.2 |≦1.5(4)

where

φ₁ : the refracting power of the first lens group, and

φ₂ : the refracting power of the second lens group.

The conditional expression (4) prescribes a proper range of a ratio ofthe refracting power of the first lens group to the refracting power ofthe second lens group.

If the upper limit value of the conditional expression (4) is violated,an entire length of the optical system undesirably becomes too large.

Whereas if the lower limit value of the conditional expression (4) isviolated, there is an undesirable increase in fluctuations both inspherical aberration and in astigmatism due to focusing.

Further, for simplifying a construction of the drive actuator fordisplacing the image position correcting lens group in the directionorthogonal to the optical axis, it is preferable that the image positioncorrecting lens group be fixed in the optical-axis direction whenfocusing. Thus, the image position correcting lens unit is fixed in theoptical-axis direction when focusing, thereby making it possible todivide the hardware structure into a focusing group and an imageposition correcting group. A degree of freedom of the design thereforeincreases.

Also, if all the positive lens elements of the first lens group are madeof the same glass material, a single-item mass production of the opticalglass can be attained, and, desirably, a reduction in unit price perlens can be expected.

On the other hand, the aberration when correcting the image position iswell compensated, and much better imaging performance is obtained. Forthis purpose, it is desirable that the closest-to-object positive lensof the image position correcting lens group satisfies the followingconditional expressions (5) through (7):

    1.43≦n.sub.d '≦1.65                          (5)

    65≦ν.sub.d '≦95                           (6)

    0.302≦θ.sub.FCd '≦0.311                (7)

where

n_(d) ': the refractive index with respect to the d-line,

ν_(d) ': the Abbe number with respect to the d-line, and

θ_(FCd) ': the partial dispersion ratio.

Note that the partial dispersion ratio θ_(FCd) ' is expressed by thefollowing formula (b):

    θ.sub.FCd '=(n.sub.d '-n.sub.c ')/(n.sub.F '-n.sub.c ')(b)

where

n_(F) ': the refractive index with respect to the F-line (λ=486.1 nm),and

n_(c) ': the refractive index with respect to the C-line (λ=656.3 nm).

The conditional expressions (5) through (7) provide conditions forprescribing proper ranges of the partial dispersion ratio, the Abbenumber and the refractive index of the closes-to-object positive lens ofthe image position correcting lens group as well as for compensating theaberration well when correcting the image position.

When deviating from the conditions of the conditional expressions (5)through (7), there is an undesirable increase in an asymmetric componentof a chromatic coma when correcting the image position. Note that alower limit of the conditional expression (5) is more preferably 1.48,and an upper limit thereof is more preferably 1.63. Further, an upperlimit of the conditional expression (7) is more preferably 0.309.

According to the present invention, the aperture stop is disposedpreferably in the vicinity of the image position correcting lens group.

Herein, it is desirable for the image position correcting lens group tobe constituted by a small number of lens elements and that the imageposition correcting lens group be disposed in the vicinity of a positionwhere a bundle of rays image-formed along the periphery of the pictureintersect the optical axis. This is because a bundle of raysimage-formed at the center of the picture are in close proximity to thebundle of rays image-formed along the periphery of the picture, and,therefore, the spherical aberration rather than an aberration relativeto a view angle may be concentratedly compensated.

Further, it is desirable for improving a balance of the lateralaberration along the periphery of the picture that the aperture stop bedisposed in a position where substantially the center of the bundle ofrays image-formed along the periphery of the picture intersects theoptical axis.

From the above, according to the present invention, it is desirable thatthe aperture stop be disposed in the vicinity of the image positioncorrecting lens group.

Also, for simplifying the layout of the lens elements, the opticalsystem is desirably constructed of the first lens group having thepositive refracting power and the second lens group having the negativerefracting power, which is defined as a minimum structure of thetelephoto type optical system. In this case, the focusing is effected bythe second lens group having the negative refracting power, and it isdesirable that the image position be corrected by displacing a part oflens subunits of the first lens group fixed during the focusing in thedirection orthogonal to the optical axis.

Further, for increasing the aperture of the optical system and attainingthe down-sizing by decreasing the entire length thereof, it is desirablethat the optical system be constructed of the first lens group havingthe positive refracting power, the second lens group having the negativerefracting power and the third lens group having the positive refractingpower. In this instance, the focusing is conducted by the second lensgroup having the negative refracting power, while the image position iscorrected by the third lens group having the positive refracting power.

Moreover, it is desirable for simplifying the assembly that the driveactuator for correcting the image position be constructed integrallywith the aperture stop.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will becomeapparent during the following discussion in conjunction with theaccompanying drawings, in which:

FIG. 1 is a view illustrating a configuration of an image positioncorrecting optical system in accordance with a first embodiment of thepresent invention;

FIG. 2 is a diagram showing a variety of aberrations in an infinityfocusing state in the first embodiment of FIG. 1;

FIG. 3 is a diagram showing the various aberrations in a closestfocusing state in the first embodiment of FIG. 1;

FIG. 4 is a view illustrating a configuration of the image positioncorrecting optical system in a second embodiment of the presentinvention;

FIG. 5 is a diagram showing the various aberrations in the infinityfocusing state in the second embodiment of FIG. 4;

FIG. 6 is a diagram showing the various aberrations in the closestfocusing state in the second embodiment of FIG. 4;

FIG. 7 is a view illustrating a configuration of the image positioncorrecting optical system in a third embodiment of the presentinvention;

FIG. 8 is a diagram showing the various aberrations in the infinityfocusing state in the third embodiment of FIG. 7;

FIG. 9 is a diagram showing the various aberrations in the closestfocusing state in the third embodiment of FIG. 7;

FIG. 10 is a view illustrating a configuration of the image positioncorrecting optical system in a fourth embodiment of the presentinvention;

FIG. 11 is a diagram showing the various aberrations in the infinityfocusing state in the fourth embodiment of FIG. 10;

FIG. 12 is a diagram showing the various aberrations in the closestfocusing state in the fourth embodiment of FIG. 10;

FIG. 13 is a view illustrating a configuration of the image positioncorrecting optical system in a fifth embodiment of the presentinvention;

FIG. 14 is a diagram showing the various aberrations in the infinityfocusing state in the fifth embodiment of FIG. 13;

FIG. 15 is a diagram showing the various aberrations in the closestfocusing state in the fifth embodiment of FIG. 13;

FIG. 16 is a view illustrating a configuration of the image positioncorrecting optical system in a sixth embodiment of the presentinvention;

FIG. 17 is a diagram showing the various aberrations in the infinityfocusing state in the sixth embodiment of FIG. 16; and

FIG. 18 is a diagram showing the various aberrations in the closestfocusing state in the sixth embodiment of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Each of the image position correcting optical systems in accordance withfirst to third embodiments of the present invention is constructed of,sequentially from an object side, a first lens group G1 having positiverefracting power, a second lens group G2 having negative refractingpower and a third lens group G3 having positive refracting power. Whenfocusing, the first and third lens groups G1, G3 are fixed, while thesecond lens group G2 moves along an optical axis. Then, the third lensgroup G3 is moved in a direction substantially orthogonal to the opticalaxis, thus correcting an image position. As explained above, the imageposition correcting optical system in the first to third embodiments isdefined as an optical system of an inner focus telephoto type which hasa positive/negative/positive refracting power layout.

On the other hand, each of image position correcting optical systems inaccordance with fourth to sixth embodiments is constructed of,sequentially from the object side, the first lens group G1 havingpositive refracting power and the second lens group G2 having negativerefracting power. Then, the first lens group G1 consists of a front lensgroup G11 having positive refracting power and a rear lens group G12having positive refracting power. When focusing, the first lens group G1is fixed, while the second lens group G2 moves along the optical axis.Each of the image position correcting optical systems in accordance withthe fourth through sixth embodiments corrects the image position bymoving the rear lens group G12 of the first lens group G1 in thedirection substantially orthogonal to the optical axis. As describedabove, each of the image position correcting optical systems in thefourth through sixth embodiments is an optical system of a rear focustelephoto type which has a positive/negative refracting power layout.

The respective embodiments of the present invention will hereinafter bediscussed with reference to the accompanying drawings.

[First Embodiment]

FIG. 1 is a view illustrating a configuration of the image positioncorrecting optical system in accordance with the first embodiment ofthis invention.

The illustrated image position correcting optical system is constructedof, sequentially from the object, a first lens group G1 including apositive meniscus lens with its convex surface toward the object side, abiconvex lens, a biconcave lens and a cemented lens having a negativemeniscus lens with its convex surface toward the object side and apositive meniscus lens with its convex surface toward the object side, asecond lens group G2 including a cemented lens of a biconvex lens and abiconcave lens and a biconcave lens and a third lens group G3 includinga negative meniscus lens with its concave surface toward the object sideand a positive meniscus lens with its concave surface toward the objectside.

Note that an aperture stop S, a fixed stop FS and a filter are providedon the image side of the third lens group G3.

Referring to FIG. 1, the second lens group G2 is so formed as to bemovable in a direction along the optical axis. The focusing is performedby moving this second lens unit along the optical axis. Further, thethird lens group G3 is so formed as to be movable in the directionsubstantially orthogonal to the optical axis. Then, an unillustrateddrive actuator moves this third lens group G3 in the directionsubstantially orthogonal to the optical axis, thereby correcting a shakeof the image position that is attributed to a vibration of the opticalsystem. As this type of drive actuator, there can be applied an actuatordisclosed in U.S. Ser. No. 08/628,192 (a continuation of Ser. No.08/417,473, abandoned, which is a continuation of Ser. No. 08/129,580,abandoned, which a continuation of Ser. No. 07/853,256), abandoned,which is assigned to the same assignee as the present application, andthe disclosure of which is hereby incorporated by reference.

The following Table 1 shows values of data in the first embodiment ofthe present invention. In Table 1, f designates the focal length in aninfinity focusing state, and F_(No) represents the F-number in theinfinity focusing state. Further, the numeral at the left end denotesthe order of each lens surface from the object side, r designates theradius of curvature of each lens surface, d represents the intervalbetween the lens surfaces, n and ν respectively designate the refractiveindex with respect to the d-line (λ=587.6 nm) and the Abbe number, andθ_(FCd) represents the partial dispersion ratio.

                  TABLE 1                                                         ______________________________________                                        f = 297                                                                       F.sub.NO = 2.88                                                                    r         d            ν  n      θ.sub.FCd                      ______________________________________                                         1   113.388   17.600       82.52 1.49782                                                                              0.305                                 2   1895.819  0.800                                                           3   110.302   18.100       82.52 1.49782                                                                              0.305                                 4   -392.025  3.500                                                           5   -331.110  4.700        35.19 1.74950                                      6   402.263   28.300                                                          7   90.170    2.200        55.60 1.69680                                      8   38.696    15.000       69.98 1.51860                                                                              0.308                                 9   213.858   (d9 = variable)                                                10   473.173   8.400        33.89 1.80384                                     11   -78.249   2.000        60.64 1.60311                                     12   99.260    5.100                                                          13   -160.670  2.000        52.30 1.74810                                     14   69.079    (d14 = variable)                                               15   146.496   6.900        69.98 1.51860                                                                              0.308                                16   -69.633   1.600                                                          17   -50.657   6.500        25.50 1.80458                                     18   -200.310  5.500                                                          19   -295.036  5.600        28.19 1.74000                                     20   -64.431   17.700                                                         21   ∞   16.000                                                         22   ∞   5.500                                                          23   ∞   2.000        64.10 1.51680                                     24   ∞   77.700                                                         ______________________________________                                        (Variable interval when focusing)                                                    Infinity Closest Focusing Distance (β = -0.13)                    ______________________________________                                        d9      5.34955 14.57183                                                      d14    13.91878  4.69650                                                      ______________________________________                                        (Condition Corresponding Values)                                              φ.sub.1 = 1/145.00597 = 0.00690                                           |φ.sub.2 | = 1/57.96812 = 0.01725                       (1) n.sub.d =                                                                              1.498      1.498      1.519                                      (2) ν.sub.d =                                                                           82.5       82.5       70.0                                       (3) θ.sub.FCd =                                                                      0.305      0.305      0.308                                      (4) φ.sub.1 / |φ.sub.2 | =                                       0.400                                                            (5) n.sub.d ' =                                                                            1.519                                                            (6) ν.sub.d ' =                                                                         70.0                                                             (7) θ.sub.FCd ' =                                                                    0.308                                                            ______________________________________                                    

Note that n_(d), ν_(d) and θ_(FCd) indicate condition correspondingvalues in the sequence of the first, second and third positive lensesfrom the object side of the first lens group.

    ______________________________________                                        (Image position correcting data)                                                       Infinity Focusing                                                                          Closest Focusing                                                 State        State                                                   ______________________________________                                        Image Position                                                                            1.0 mm (Maximum)                                                                             1.0 mm (Maximum)                                   Correcting Dis-                                                               placement Quan-                                                               tity                                                                          Corresponding                                                                            +1.0 mm (Maximum)                                                                            +1.0 mm (Maximum)                                   Image Moving                                                                  Quantity                                                                      ______________________________________                                    

Note that the plus sign of the image moving quantity indicates that theimage moves in the same direction as a displacement direction of theimage position correcting lens group.

FIGS. 2 and 3 are diagrams respectively showing various aberrations inthe infinity focusing state and in the closest focusing state. Referringto the individual aberration diagrams, F_(NO) represents the F-number, Ydesignates the image height, D denotes the d-line (λ=587.6 nm), Cdesignates the C-line (λ=656.3 nm), F indicates the F-line (λ=486.1 nm),and G represents the g-line (λ=435.6 nm).

Note that the solid line represents the sagittal image surface, and thebroken line indicates the meridional image surface in the aberrationdiagram showing an astigmatism. Further, the broken line represents thesine condition in the aberration diagram illustrating a sphericalaberration. In the aberration diagram showing a chromatic difference ofmagnification, the d-line is fiducial.

Moreover, in the aberration diagram illustrating a lateral aberrationwhen correcting the image position, the image position correctingdisplacement quantity is 1 mm at the maximum.

As is obvious from the respective aberration diagrams, it can beunderstood that the various aberrations are well compensated includingthe time when correcting the image position in accordance with thisembodiment.

[Second Embodiment]

FIG. 4 is a view illustrating a configuration of the image positioncorrecting optical system in accordance with the second embodiment ofthis invention.

The illustrated image position correcting optical system is constructedof, sequentially from the object, a first lens group G1 including apositive meniscus lens with its convex surface toward the object side, abiconvex lens, a biconcave lens and a cemented lens having a negativemeniscus lens with its convex surface toward the object side and apositive meniscus lens with its convex surface toward the object side, asecond lens group G2 including a cemented lens having a biconvex lensand a biconcave lens and a biconcave lens and a third lens group G3including a biconvex lens, a negative meniscus lens with its concavesurface toward the object side and a positive meniscus lens with itsconcave surface toward the object side.

Note that the aperture stop S, the fixed stop FS and the filter areprovided on the image side of the third lens group G3.

Referring to FIG. 4, the second lens group G2 is so formed as to bemovable in the direction along the optical axis. The focusing isperformed by moving this second lens group along the optical axis.Further, the third lens group G3 is so formed as to be movable in thedirection substantially orthogonal to the optical axis. Then, theunillustrated drive actuator, in the same way as in the first embodimentdiscussed above, moves this third lens group G3 in the directionsubstantially orthogonal to the optical axis, thereby correcting theshake of the image position that is attributed to the vibration of theoptical system.

The image position correcting optical system in the second embodimenthas the same configuration as the image position correcting opticalsystem in the first embodiment discussed above, but the refracting powerand the shape in each lens unit are different.

The following Table 2 shows values of data in the second embodiment ofthe present invention. In Table 2, f designates the focal length in aninfinity focusing state, and F_(NO) represents the F-number in theinfinity focusing state. Further, the numeral at the left end denotesthe order of each lens surface from the object side, r designates theradius of curvature of each lens surface, d represents the intervalbetween the lens surfaces, n and ν respectively designate the refractiveindex with respect to the d-line (λ=587.6 nm) and the Abbe number, andθ_(FCd) represents the partial dispersion ratio.

                  TABLE 2                                                         ______________________________________                                        f = 297                                                                       F.sub.NO = 2.88                                                                    r         d            ν  n      θ.sub.FCd                      ______________________________________                                         1   113.713   17.600       82.52 1.49782                                                                              0.305                                 2   6080.230  0.500                                                           3   107.910   18.100       94.97 1.43875                                                                              0.307                                 4   -391.820  3.600                                                           5   -337.603  4.700        35.19 1.74950                                      6   556.672   30.100                                                          7   98.675    2.200        55.60 1.69680                                      8   35.118    15.000       67.87 1.59319                                                                              0.303                                 9   162.573   (d9 = variable)                                                10   455.161   8.400        33.89 1.80384                                     11   -78.338   2.000        60.64 1.60311                                     12   99.362    5.100                                                          13   -163.088  2.000        52.30 1.74810                                     14   68.110    (d14 = variable)                                               15   146.892   6.900        69.98 1.51860                                                                              0.308                                16   -70.772   1.600                                                          17   -51.780   6.500        25.50 1.80458                                     18   -195.577  5.500                                                          19   -307.115  5.600        28.19 1.74000                                     20   -66.527   17.700                                                         21   ∞   16.000                                                         22   ∞   5.500                                                          23   ∞   2.000        64.10 1.51680                                     24   ∞   77.2952                                                        ______________________________________                                        (Variable interval when focusing)                                                    Infinity Closest Focusing Distance (β = -0.13)                    ______________________________________                                        d9      3.51504 12.73732                                                      d14    14.34629  5.12401                                                      ______________________________________                                        (Condition Corresponding Values)                                              φ.sub.1 = 1/145.00516 = 0.00690                                           |φ.sub.2 | = 1/57.96812 = 0.01725                       (1) n.sub.d =                                                                              1.498      1.439      1.593                                      (2) ν.sub.d =                                                                           82.5       95.0       67.9                                       (3) θ.sub.FCd =                                                                      0.305      0.307      0.303                                      (4) φ.sub.1 / |φ.sub.2 | =                                       0.400                                                            (5) n.sub.d ' =                                                                            1.519                                                            (6) ν.sub.d ' =                                                                         70.0                                                             (7) θ.sub.FCd ' =                                                                    0.308                                                            ______________________________________                                    

Note that n_(d), ν_(d) and θ_(FCd) indicate the condition correspondingvalues in the sequence of the first, second and third positive lensesfrom the object side of the first lens group.

    ______________________________________                                        (Image position correcting data)                                                       Infinity Focusing                                                                          Closest Focusing                                                 State        State                                                   ______________________________________                                        Image Position                                                                            1.0 mm (Maximum)                                                                             1.0 mm (Maximum)                                   Correcting Dis-                                                               placement Quan-                                                               tity                                                                          Corresponding                                                                            +1.0 mm (Maximum)                                                                            +1.0 mm (Maximum)                                   Image Moving                                                                  Quantity                                                                      ______________________________________                                    

Note that the plus sign of the image moving quantity indicates that theimage moves in the same direction as the displacement direction of theimage position correcting lens group.

FIGS. 5 and 6 are diagrams respectively showing various aberrations inthe infinity focusing state and in the closest focusing state. Referringto the individual aberration diagrams, F_(NO) represents the F-number, Ydesignates the image height, D denotes the d-line (λ=587.6 nm), Cdenotes the C-line (λ=656.3 nm), F represents the F-line (λ=486.1 nm),and G represents the g-line (λ=435.6 nm).

Note that the solid line represents the sagittal image surface, and thebroken line indicates the meridional image surface in the aberrationdiagram showing the astigmatism. Further, the broken line represents thesine condition in the aberration diagram illustrating the sphericalaberration. In the aberration diagram showing the chromatic differenceof magnification, the d-line is fiducial.

Moreover, in the aberration diagram illustrating the lateral aberrationwhen correcting the image position, the image position correctingdisplacement quantity is 1 mm at the maximum.

As is obvious from the respective aberration diagrams, it can beunderstood that the various aberrations are well compensated includingthe time when correcting the image position in accordance with thisembodiment.

[Third Embodiment]

FIG. 7 is a view illustrating a configuration of the image positioncorrecting optical system in accordance with the third embodiment ofthis invention.

The illustrated image position correcting optical system is constructedof, sequentially from the object, a first lens group G1 including apositive meniscus lens with its convex surface toward the object side, abiconvex lens, a biconcave lens and a cemented lens having a negativemeniscus lens with its convex surface toward the object side and apositive meniscus lens with its convex surface toward the object side, asecond lens group G2 including a biconcave lens and a cemented lenshaving a positive meniscus lens with its concave surface toward theobject side and a biconvex lens and a third lens group G3 including abiconvex lens, a negative meniscus lens with its concave surface towardthe object side and a positive meniscus lens with its concave surfacetoward the object side.

Note that the aperture stop S is provided between the second lens groupG2 and the third lens group G3, while the fixed stop FS and the filterare provided on the image side of the third lens group G3.

Referring to FIG. 7, the second lens group G2 is so formed as to bemovable in the direction along the optical axis. The focusing isperformed by moving this second lens group along the optical axis.Further, the third lens group G3 is so formed as to be movable in thedirection substantially orthogonal to the optical axis. Then, theunillustrated drive actuator, in the same way as in the first embodimentdiscussed above, moves this third lens group G3 in the directionsubstantially orthogonal to the optical axis, thereby correcting theshake of the image position that is attributed to the vibration of theoptical system.

The image position correcting optical system in the third embodiment hasthe same configuration as the image position correcting optical systemin the first embodiment discussed above, but the refracting power andthe shape in each lens group are different. Note that all the positivelenses of the first lens group G1 are composed of the same glass in thisembodiment.

The following Table 3 shows values of data in the third embodiment ofthe present invention. In Table 3, f designates the focal length in aninfinity focusing state, and F_(NO) represents the F-number in theinfinity focusing state. Further, the numeral at the left end denotesthe order of each lens surface from the object side, r designates theradius of curvature of each lens surface, d represents the intervalbetween the lens surfaces, n and ν respectively designate the refractiveindex with respect to the d-line (λ=587.6 nm) and the Abbe number, andθ_(FCd) represents the partial dispersion ratio.

                  TABLE 3                                                         ______________________________________                                        f = 588                                                                       F.sub.NO = 2.88                                                                    r         d            ν  n      θ.sub.FCd                      ______________________________________                                         1   281.150   23.400       82.52 1.49782                                                                              0.305                                 2   11960.780 24.200                                                          3   253.845   30.600       82.52 1.49782                                                                              0.305                                 4   -826.472  7.400                                                           5   -749.631  9.800        40.90 1.79631                                      6   721.627   83.000                                                          7   175.498   7.000        52.30 1.74810                                      8   93.064    32.000       82.52 1.49782                                                                              0.305                                 9   17702.829 (d9 = variable)                                                10   -332.270  4.600        54.01 1.61720                                     11   145.367   7.400                                                          12   -544.504  12.600       33.89 1.80384                                     13   -75.204   4.600        54.01 1.61720                                     14   131.023   (d14 = variable)                                               15   ∞   6.000        (stop)                                            16   296.071   10.600       69.98 1.51860                                                                              0.308                                17   -145.438  5.000                                                          18   -76.183   9.400        33.89 1.80384                                     19   -114.376  13.200                                                         20   -258.532  9.000        65.77 1.46450                                     21   -90.765   19.600                                                         22   ∞   41.400                                                         23   ∞   4.000        64.10 1.51680                                     24   ∞   35.024                                                         25   ∞   83.999                                                         ______________________________________                                        (Variable interval when focusing)                                                    Infinity Closest Focusing Distance (β = -0.14)                    ______________________________________                                        d9     53.87566 75.70128                                                      d14    43.03719 21.21157                                                      ______________________________________                                        (Condition Corresponding Values)                                              φ.sub.1 = 1/301.99141 = 0.00331                                           |φ.sub.2 | = 1/98.00000 = 0.00102                       (1) n.sub.d =                                                                              1.498      1.498      1.498                                      (2) ν.sub.d =                                                                           82.5       82.5       82.5                                       (3) θ.sub.FCd =                                                                      0.305      0.305      0.305                                      (4) φ.sub.1 / |φ.sub.2 | =                                       0.324                                                            (5) n.sub.d ' =                                                                            1.519                                                            (6) ν.sub.d ' =                                                                         70.0                                                             (7) θ.sub.FCd ' =                                                                    0.308                                                            ______________________________________                                    

Note that n_(d), ν_(d) and θ_(FCd) indicate the condition correspondingvalues in the sequence of the first, second and third positive lensesfrom the object side of the first lens group.

    ______________________________________                                        (Image position correcting data)                                                       Infinity Focusing                                                                          Closest Focusing                                                 State        State                                                   ______________________________________                                        Image Position                                                                            2.0 mm (Maximum)                                                                            2.0 mm (Maximum)                                    Correcting Dis-                                                               placement Quan-                                                               tity                                                                          Corresponding                                                                            +2.0 mm (Maximum)                                                                            +2.0 mm (Maximum)                                   Image Moving                                                                  Quantity                                                                      ______________________________________                                    

Note that the plus sign of the image moving quantity indicates that theimage moves in the same direction as the displacement direction of theimage position correcting lens unit.

FIGS. 8 and 9 are diagrams respectively showing various aberrations inthe infinity focusing state and in the closest focusing state. Referringto the individual aberration diagrams, F_(NO) represents the F-number, Ydesignates the image height, D denotes the d-line (λ=587.6 nm), Cdenotes the C-line (λ=656.3 nm), F represents the F-line (λ=486.1 nm),and G represents the g-line (λ=435.6 nm).

Note that the solid line represents the sagittal image surface, and thebroken line indicates the meridional image surface in the aberrationdiagram showing the astigmatism. Further, the broken line represents thesine condition in the aberration diagram illustrating the sphericalaberration. In the aberration diagram showing the chromatic differenceof magnification, the d-line is fiducial.

Moreover, in the aberration diagram illustrating the lateral aberrationwhen correcting the image position, the image position correctingdisplacement quantity is 2 mm at the maximum.

As is obvious from the respective aberration diagrams, it can beunderstood that the various aberrations are well compensated includingthe time when correcting the image position in accordance with thisembodiment.

[Fourth Embodiment]

FIG. 10 is a view illustrating a configuration of the image positioncorrecting optical system in accordance with the fourth embodiment ofthis invention.

The illustrated image position correcting optical system is constructedof, sequentially from the object, a first lens group G1 consisting of afront lens group G11 including a biconvex lens, a positive meniscus lenswith its convex surface toward the object side and a biconcave lens anda rear lens unit G12 including a cemented lens having a negativemeniscus lens with its convex surface toward the object side and abiconvex lens and a second lens unit G2 including a cemented lens havinga biconvex lens and a biconcave lens.

Note that the aperture stop S is provided between the first lens groupG1 and the second lens unit G2.

Referring to FIG. 10, the second lens unit G2 is so formed as to bemovable in the direction along the optical axis. The focusing isperformed by moving this second lens unit along the optical axis.Further, the rear lens unit G12 of the first lens group G1 is so formedas to be movable in the direction substantially orthogonal to theoptical axis. Then, the unillustrated drive actuator, in the same way asin the first embodiment discussed above, moves the rear lens unit G12 ofthe first lens group G1 in the direction substantially orthogonal to theoptical axis, thereby correcting the shake of the image position that isattributed to the vibration of the optical system.

Note that all the positive lenses of the first lens group G1 arecomposed of the same glass in this embodiment.

The following Table 4 shows values of data in the fourth embodiment ofthe present invention. In Table 4, f designates the focal length in aninfinity focusing state, and F_(NO) represents the F-number in theinfinity focusing state. Further, the numeral at the left end denotesthe order of each lens surface from the object side, r designates theradius of curvature of each lens surface, d represents the intervalbetween the lens surfaces, n and ν respectively designate the refractiveindex with respect to the d-line (λ=587.6 nm) and the Abbe number, andθ_(FCd) represents the partial dispersion ratio.

                  TABLE 4                                                         ______________________________________                                        f = 500                                                                       F.sub.NO = 4.50                                                                    r         d            ν  n      θ.sub.FCd                      ______________________________________                                         1   359.710   11.000       82.52 1.49782                                                                              0.305                                 2   -721.221  13.300                                                          3   243.586   11.000       82.52 1.49782                                                                              0.305                                 4   1877.620  5.300                                                           5   -763.325  7.000        33.89 1.80384                                      6   1083.988  136.700                                                         7   188.211   6.000        52.30 1.74810                                      8   95.823    14.000       82.52 1.49782                                                                              0.305                                 9   -487.464  5.000                                                          10   ∞   (d10 = variable)                                                                           (stop)                                            11   282.020   7.000        27.61 1.75520                                     12   -1923.866 4.000        53.93 1.71300                                     13   118.267   (d13 = variable)                                               ______________________________________                                        (Variable interval when focusing)                                                    Infinity Closest Focusing Distance (β = -0.11)                    ______________________________________                                        d10     1.86316  28.30228                                                     d13    253.12920                                                                              225.65168                                                     ______________________________________                                        (Condition Corresponding Values)                                              φ.sub.1 = 1/277.79717 = 0.00360                                           |φ.sub.2 | = 1/309.90210 = 0.00323                      (1) n.sub.d =                                                                              1.498      1.498      1.498                                      (2) ν.sub.d =                                                                           82.5       82.5       82.5                                       (3) θ.sub.FCd =                                                                      0.305      0.305      0.305                                      (4) φ.sub.1 / |φ.sub.2 | =                                       1.116                                                            (5) n.sub.d ' =                                                                            1.498                                                            (6) ν.sub.d ' =                                                                         82.5                                                             (7) θ.sub.FCd ' =                                                                    0.305                                                            ______________________________________                                    

Note that n_(d), ν_(d) and θ_(FCd) indicate the condition correspondingvalues in the sequence of the first, second and third positive lensesfrom the object side of the first lens group.

    ______________________________________                                        (Image position correcting data)                                                       Infinity Focusing                                                                          Closest Focusing                                                 State        State                                                   ______________________________________                                        Image Position                                                                            1.4 mm (Maximum)                                                                             1.4 mm (Maximum)                                   Correcting Dis-                                                               placement Quan-                                                               tity                                                                          Corresponding                                                                            +1.0 mm (Maximum)                                                                            +1.0 mm (Maximum)                                   Image Moving                                                                  Quantity                                                                      ______________________________________                                    

Note that the plus sign of the image moving quantity indicates that theimage moves in the same direction as the displacement direction of theimage position correcting lens unit.

FIGS. 11 and 12 are diagrams respectively showing various aberrations inthe infinity focusing state and in the closest focusing state. Referringto the individual aberration diagrams, F_(NO) represents the F-number, Ydesignates the image height, D denotes the d-line (λ=587.6 nm), Cdenotes the C-line (λ=656.3 nm), F represents the F-line (λ=486.1 nm),and G represents the g-line (λ=435.6 nm).

Note that the solid line represents the sagittal image surface, and thebroken line indicates the meridional image surface in the aberrationdiagram showing the astigmatism. Further, the broken line represents thesine condition in the aberration diagram illustrating the sphericalaberration. In the aberration diagram showing the chromatic differenceof magnification, the d-line is fiducial.

Moreover, in the aberration diagram illustrating the lateral aberrationwhen correcting the image position, the image position correctingdisplacement quantity is 1.4 mm at the maximum.

As is obvious from the respective aberration diagrams, it can beunderstood that the various aberrations are well compensated includingthe time when correcting the image position in accordance with thisembodiment.

[Fifth Embodiment]

FIG. 13 is a view illustrating a configuration of the image positioncorrecting optical system in accordance with the fifth embodiment ofthis invention.

The illustrated image position correcting optical system is constructedof, sequentially from the object, a first lens group G1 consisting of afront lens group G11 including a biconvex lens, a positive meniscus lenswith its convex surface toward the object side and a biconcave lens anda rear lens unit G12 including a cemented lens having a negativemeniscus lens with its convex surface toward the object side and abiconvex lens and a second lens group G2 including a cemented lens of abiconvex lens and negative meniscus lens with its concave surface towardthe object side and a biconcave lens.

Note that the aperture stop S is provided between the first lens groupG1 and the second lens group G2.

Referring to FIG. 13, the second lens group G2 is so formed as to bemovable in the direction along the optical axis. The focusing isperformed by moving this second lens unit along the optical axis.Further, the rear lens unit G12 of the first lens group G1 is so formedas to be movable in the direction substantially orthogonal to theoptical axis. Then, the unillustrated drive actuator, in the same way asin the first embodiment discussed above, moves the rear lens unit G12 ofthe first lens group G1 in the direction substantially orthogonal to theoptical axis, thereby correcting the shake of the image position that isattributed to the vibration of the optical system.

The image position correcting optical system in the fifth embodiment hasthe same configuration as that of the image position correcting opticalsystem in the fourth embodiment discussed above, but the refractingpower and the shape of each lens unit are different. Note that all thepositive lenses of the first lens group G1 are composed of the sameglass in this embodiment.

The following Table 5 shows values of data in the fifth embodiment ofthe present invention. In Table 5, f designates the focal length in aninfinity focusing state, and F_(NO) represents the F-number in theinfinity focusing state. Further, the numeral at the left end denotesthe order of each lens surface from the object side, r designates theradius of curvature of each lens surface, d represents the intervalbetween the lens surfaces, n and ν respectively designate the refractiveindex with respect to the d-line (λ=587.6 nm) and the Abbe number, andθ_(FCd) represents the partial dispersion ratio.

                  TABLE 5                                                         ______________________________________                                        f = 500                                                                       F.sub.NO = 4.50                                                                    r         d            ν  n      θ.sub.FCd                      ______________________________________                                         1   354.655   11.000       82.52 1.49782                                                                              0.305                                 2   -1065.552 0.300                                                           3   220.008   11.000       82.52 1.49782                                                                              0.305                                 4   950.837   4.000                                                           5   -725.711  7.000        33.89 1.80384                                      6   1707.433  100.000                                                         7   233.153   6.000        52.30 1.74810                                      8   106.766   14.000       82.52 1.49782                                                                              0.305                                 9   -412.376  7.000                                                          10   ∞   (d10 = variable)                                                                           (stop)                                            11   671.262   8.000        32.17 1.67270                                     12   -229.884  4.000        54.55 1.51454                                     13   -445.690  3.800                                                          14   -314.979  5.000        54.55 1.51454                                     15   12.678    (d15 = variable)                                               ______________________________________                                        (Variable interval when focusing)                                                    Infinity Closest Focusing Distance (β = -0.11)                    ______________________________________                                        d10     22.22325                                                                               48.66237                                                     d15    255.32220                                                                              228.35704                                                     ______________________________________                                        (Condition Corresponding Values)                                              φ.sub.1 = 1/277.79675 = 0.00360                                           |φ.sub.2 | = 1/309.90423 = 0.00323                      (1) n.sub.d =                                                                              1.498      1.498      1.498                                      (2) ν.sub.d =                                                                           82.5       82.5       82.5                                       (3) θ.sub.FCd =                                                                      0.305      0.305      0.305                                      (4) φ.sub.1 / |φ.sub.2 | =                                       1.116                                                            (5) n.sub.d ' =                                                                            1.498                                                            (6) ν.sub.d ' =                                                                         82.5                                                             (7) θ.sub.FCd ' =                                                                    0.305                                                            ______________________________________                                    

Note that n_(d), ν_(d) and θ_(FCd) indicate the condition correspondingvalues in the sequence of the first, second and third positive lensesfrom the object side of the first lens unit.

    ______________________________________                                        (Image position correcting data)                                                       Infinity Focusing                                                                          Closest Focusing                                                 State        State                                                   ______________________________________                                        Image Position                                                                            1.4 mm (Maximum)                                                                             1.4 mm (Maximum)                                   Correcting Dis-                                                               placement Quan-                                                               tity                                                                          Corresponding                                                                            +1.0 mm (Maximum)                                                                            +1.0 mm (Maximum)                                   Image Moving                                                                  Quantity                                                                      ______________________________________                                    

Note that the plus sign of the image moving quantity indicates that theimage moves in the same direction as the displacement direction of theimage position correcting lens unit.

FIGS. 14 and 15 are diagrams respectively showing various aberrations inthe infinity focusing state and in the closest focusing state. Referringto the individual aberration diagrams, F_(NO) represents the F-number, Ydesignates the image height, D denotes the d-line (λ=587.6 nm), Cdenotes the C-line (λ=656.3 nm), F represents the F-line (λ=486.1 nm),and G represents the g-line (λ=435.6 nm).

Note that the solid line represents the sagittal image surface, and thebroken line indicates the meridional image surface in the aberrationdiagram showing the astigmatism. Further, the broken line represents thesine condition in the aberration diagram illustrating the sphericalaberration. In the aberration diagram showing the chromatic differenceof magnification, the d-line is fiducial.

Moreover, in the aberration diagram illustrating the lateral aberrationwhen correcting the image position, the image position correctingdisplacement quantity is 1.4 mm at the maximum.

As is obvious from the respective aberration diagrams, it can beunderstood that the various aberrations are well compensated includingthe time when correcting the image position in accordance with thisembodiment.

[Sixth Embodiment]

FIG. 16 is a view illustrating a configuration of the image positioncorrecting optical system in accordance with the sixth embodiment ofthis invention.

The illustrated image position correcting optical system is constructedof, sequentially from the object, a first lens group G1 consisting of afront lens group G11 including a biconvex lens, a biconcave lens and abiconvex lens and a rear lens unit G12 including a cemented lens havinga negative meniscus lens with its convex surface toward the object sideand a biconvex lens and a second lens group G2 including a positivemeniscus lens with its concave surface toward the object side and abiconcave lens.

Note that the aperture stop S is provided between the first lens unit G1and the second lens group G2.

Referring to FIG. 16, the second lens group G2 is so formed as to bemovable in the direction along the optical axis. The focusing isperformed by moving this second lens unit along the optical axis.Further, the rear lens unit G12 of the first lens group G1 is so formedas to be movable in the direction substantially orthogonal to theoptical axis. Then, the unillustrated drive actuator, in the same way asin the first embodiment discussed above, moves the rear lens unit G12 ofthe first lens group G1 in the direction substantially orthogonal to theoptical axis, thereby correcting the shake of the image position that isattributed to the vibration of the optical system.

The image position correcting optical system in the sixth embodiment hasthe same configuration as that of the image position correcting opticalsystem in the fourth embodiment discussed above, but the refractingpower and the shape of each lens unit are different.

The following Table 6 shows values of data in the sixth embodiment ofthe present invention. In Table 6, f designates the focal length in aninfinity focusing state, and F_(NO) represents the F-number in theinfinity focusing state. Further, the numeral at the left end denotesthe order of each lens surface from the object side, r designates theradius of curvature of each lens surface, d represents the intervalbetween the lens surfaces, n and ν respectively designate the refractiveindex with respect to the d-line (λ=587.6 nm) and the Abbe number, andθ_(FCd) represents the partial dispersion ratio.

                  TABLE 6                                                         ______________________________________                                        f = 500                                                                       F.sub.NO = 4.50                                                                    r         d            ν  n      θ.sub.FCd                      ______________________________________                                         1   295.709   12.100       82.52 1.49782                                                                              0.305                                 2   -424.620  3.000                                                           3   -332.634  7.700        46.54 1.80411                                      4   3185.473  0.100                                                           5   307.788   12.100       82.52 1.49782                                                                              0.305                                 6   -4999.439 145.500                                                         7   216.565   6.600        46.54 1.80411                                      8   96.311    15.400       67.87 1.59319                                                                              0.303                                 9   -1302.324 4.000                                                          10   ∞   (d10 = variable)                                                                           (stop)                                            11   -1908.639 8.560        37.90 1.72342                                     12   -263.102  25.200                                                         13   -172.006  5.350        65.77 1.46450                                     14   153.765   (d14 = variable)                                               ______________________________________                                        (Variable interval when focusing)                                                    Infinity Closest Focusing Distance (β = -0.11)                    ______________________________________                                        d10     6.43030  42.56250                                                     d15    229.96210                                                                              193.80311                                                     ______________________________________                                        (Condition Corresponding Values)                                              φ.sub.1 = 1/305.57525 = 0.00327                                           |φ.sub.2 | = 1/331.59831 = 0.00302                      (1) n.sub.d =                                                                              1.498      1.498      1.593                                      (2) ν.sub.d =                                                                           82.5       82.5       67.9                                       (3) θ.sub.FCd =                                                                      0.305      0.305      0.303                                      (4) φ.sub.1 / |φ.sub.2 | =                                       1.084                                                            (5) n.sub.d ' =                                                                            1.593                                                            (6) ν.sub.d ' =                                                                         67.9                                                             (7) θ.sub.FCd ' =                                                                    0.303                                                            ______________________________________                                    

Note that n_(d), ν_(d) and θ_(FCd) indicate the condition correspondingvalues in the sequence of the first, second and third positive lensesfrom the object side of the first lens group.

    ______________________________________                                        (Image position correcting data)                                                       Infinity Focusing                                                                          Closest Focusing                                                 State        State                                                   ______________________________________                                        Image Position                                                                            1.4 mm (Maximum)                                                                            1.4 mm (Maximum)                                    Correcting Dis-                                                               placement Quan-                                                               tity                                                                          Corresponding                                                                            +1.0 mm (Maximum)                                                                            +1.0 mm (Maximum)                                   Image Moving                                                                  Quantity                                                                      ______________________________________                                    

Note that the plus sign of the image moving quantity indicates that theimage moves in the same direction as the displacement direction of theimage position correcting lens unit.

FIGS. 17 and 18 are diagrams respectively showing various aberrations inthe infinity focusing state and in the closest focusing state. Referringto the individual aberration diagrams, F_(NO) represents the F-number, Ydesignates the image height, D denotes the d-line (λ=587.6 nm), Cdenotes the C-line (λ=656.3 nm), F represents the F-line (λ=486.1 nm),and G represents the g-line (λ=435.6 nm).

Note that the solid line represents the sagittal image surface, and thebroken line indicates the meridional image surface in the aberrationdiagram showing the astigmatism. Further, the broken line represents thesine condition in the aberration diagram illustrating the sphericalaberration. In the aberration diagram showing the chromatic differenceof magnification, the d-line is fiducial.

Moreover, in the aberration diagram illustrating the lateral aberrationwhen correcting the image position, the image position correctingdisplacement quantity is 1.4 mm at the maximum.

As is obvious from the respective aberration diagrams, it can beunderstood that the various aberrations are well compensated includingthe time when correcting the image position in accordance with thisembodiment.

Note that the moving quantity on the image surface is set to 1.0 mm inthe first through sixth embodiments discussed above but may be larger orsmaller than this value.

As discussed above, in accordance with the respective embodiments of thepresent invention, the image position correcting optical systemexhibiting a good imaging performance (especially about the chromaticaberration) can be actualized by employing only the optical glassmaterial advantageous in terms of a mass productivity without increasingthe number of the lens elements constituting the whole optical systems.

It is apparent that, in this invention, a wide range of differentworking modes can be formed based on the invention without deviatingfrom the spirit and scope of the invention. This invention is notrestricted by its specific working modes except being limited by theappended claims.

What is claimed is:
 1. An image position correcting optical system,comprising, sequentially from an object side:a first lens group havingpositive refracting power; and a second lens group having negativerefracting power, wherein said first lens group is fixed so as not to bemovable along an optical axis, said second lens group is provided so asto be movable along the optical axis, a lens subgroup selected from lenselements constituting said first lens group is so provided as to bemovable in a direction transverse to the optical axis, and a positivelens element of the lens elements constituting said first lens groupsatisfies the following conditions:
 1. 43≦n_(d) ≦1.65

    65≦ν.sub.d ≦95

    0.302≦θ.sub.FCd ≦0.309

where n_(d) is the refractive index with respect to the d-line, n_(F) isthe refractive index with respect to the F-line, n_(c) is the refractiveindex with respect to the C-line, ν_(d) is the Abbe number with respectto the d-line, and θ_(FCd) is the partial dispersion ratio expressed by(n_(d) -n_(c)) / (n_(F) -n_(c)).
 2. An image position correcting opticalsystem according to claim 1, wherein said optical system satisfies thefollowing condition:

    0.2≦φ.sub.1 /|φ.sub.2 |≦1.5

where φ₁ is the refracting power of said first lens group, and φ₂ is therefracting power of said second lens group.
 3. An image positioncorrecting optical system according to claim 1, wherein said first lensgroup has a front lens group exhibiting positive refracting power and arear lens group exhibiting positive refracting power, and said rear lensgroup is the lens subgroup movable in the direction transverse to theoptical axis.
 4. An image position correcting optical system accordingto claim 1, wherein all positive lens elements among the lens elementsconstituting said first lens group are made of the same material.
 5. Animage position correcting optical system according to claim 1, wherein aclosest-to-object positive lens element in said lens subgroup movable inthe direction transverse to the optical axis satisfies the followingconditions:

    1.48≦n.sub.d '≦1.63

    65≦ν.sub.d '≦95

    0.302≦θ.sub.FCd '≦0.309

where n_(d) ' is the refractive index with respect to the d-line, n_(F)' is the refractive index with respect to the F-line, n_(c) ' is therefractive index with respect to the C-line, ν_(d) ' is the Abbe numberwith respect to the d-line, and θ_(FCd) ' is the partial dispersionratio expressed by (n_(d) '-n_(c) ') / (n_(F) '-n_(c) ').
 6. An imageposition correcting optical system according to claim 1, wherein anaperture stop is disposed in the vicinity of said lens subgroup movablein the direction transverse to the optical axis.
 7. An image positioncorrecting optical system according to claim 6, wherein a drive actuatorfor driving said lens subgroup movable in the direction transverse tothe optical axis is constructed integrally with said aperture stop.